BEIJING , China -LRB- CNN -RRB- -- The head of China 's quality watchdog is reported to have resigned over the tainted baby milk scandal that has killed four children and sickened nearly 53,000 others .

The official Xinhua News Agency said Li Changjiang had quit with the approval of China 's State Council . Li 's agency is responsible for ensuring that China 's food supply chain is safe .

Monday 's resignation came hours after the World Health Organization said the scandal had highlighted flaws in the country 's entire food supply chain .

The chemical melamine blamed for causing kidney stones and kidney failure has been detected in formula milk powder from 22 dairies across China .

The crisis was initially thought to have been confined to baby milk powder , but tests have found melamine in samples of liquid milk taken from China 's two largest dairy producers , Mengniu Dairy Group and Yili Industrial Group , as well as Shanghai-based Bright Dairy .

WHO China representative Hans Troedsson said on Monday quality issues could occur anywhere from the farm to the retail outlet .

He said `` it 's clearly something that is not acceptable and needs to be rectified and corrected , '' according to The Associated Press . Troedsson said the WHO was discussing with officials how to strengthen China 's food quality system .

Chinese Premier Wen Jiabao has called milk manufacturers `` heartless '' and promised stricter laws to protect the public .

China 's Health Ministry said Sunday that about 13,000 children were hospitalized , while another 40,000 had undergone outpatient treatment for illnesses related to suspected melamine-tainted milk products .

The scandal has spread beyond the mainland with melamine being found in three Chinese-made dairy products in Singapore .

The country 's Agri-Food and Veterinary Authority said tests on `` White Rabbit Creamy Candy '' showed that it was contaminated with melamine and it ordered stores to remove the product from shelves .

Taiwan announced Monday it was banning the importation of all dairy products from China because of melamine contamination in milk supplies on the mainland , Taiwan 's Health Ministry said Monday .

And a second child in Hong Kong has been diagnosed with a kidney stones after drinking the tainted milk as worried parents continued to take their children for health checkups , the government said Monday , AP reported .

The 4-year-old boy was in hospital in a stable condition , the Hong Kong government said in a statement . A three-year-old girl was sickened by a suspected melamine-tainted milk over the weekend -- the first known illness outside of mainland China .

The Chinese premier visited Beijing hospitals and a supermarket Sunday to show his concern for the crisis .

`` What we need to do now is to ensure that nothing like this happens in the future , not only in dairy products , but in all foods , '' he said . `` Manufacturers and owners of dairy companies should show more morality and social responsibility in these cases . They are heartless , so we have to create strict law and legislation . I 'm sorry . ''

Investigators arrested two brothers who sold milk used to produce the contaminated baby milk powder last week . They could face death if convicted , according to China Daily , a state-run newspaper .

The raw milk had been watered down and the chemical added to fool quality checks , the newspaper said . Melamine is commonly used in coatings and laminates , wood adhesives , fabric coatings , ceiling tiles and flame retardants . Watch CNN visit the company at the center of the scandal ''

But anger has been directed not just at the producers accused of adulterating their milk to increase profits , but also at government regulators , Time magazine reported .

`` Xinhua was quick to blame the dairy industry for their skewed rules , but what it did n't say was that the government also played a part in that ugly game , '' the magazine quoted a blogger , identified as sadmoon109 , as saying .

Health experts say ingesting melamine can lead to kidney stones , urinary tract ulcers , and eye and skin irritation . It also robs infants of much-needed nutrition .

Thousands of tons of the tainted milk powder have been recalled .

Melamine is the same industrial contaminant from China that poisoned and killed thousands of U.S. dogs and cats last year .

The chemical , a byproduct of plastic manufacturing , can be used to mimic high-protein additives . Learn more about the chemical melamine ''

A senior dairy analyst said Chinese farmers were cutting corners to cope with rising costs for feed and labor .

`` Before the melamine incident , I know they could have been adding organic stuff , say animal urine or skin , '' Chen Lianfang of Beijing Orient Agribusiness Consultant told Time .

`` Basically , anything that can boost the protein reading . ''

Copyright 2008 CNN . All rights reserved.This material may not be published , broadcast , rewritten , or redistributed . Associated Press contributed to this report .

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Head of China 's quality watchdog resigns over tainted baby formula scandal

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WHO representative said scandal shows up flaws in China 's food supply chain

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Four infants in China dead , 53,000 reported ill from tainted milk powder